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.Dd $Mdocdate: September 18 2023 $
.Dt PEM_READ 3
.Os
.Sh NAME
.Nm PEM_write ,
.Nm PEM_write_bio ,
.Nm PEM_read ,
.Nm PEM_read_bio ,
.Nm PEM_get_EVP_CIPHER_INFO ,
.Nm PEM_do_header ,
.Nm PEM_def_callback ,
.Nm pem_password_cb
.Nd PEM encoding routines
.Sh SYNOPSIS
.In openssl/pem.h
.Ft int
.Fo PEM_write
.Fa "FILE *fp"
.Fa "const char *name"
.Fa "const char *header"
.Fa "const unsigned char *data"
.Fa "long len"
.Fc
.Ft int
.Fo PEM_write_bio
.Fa "BIO *bp"
.Fa "const char *name"
.Fa "const char *header"
.Fa "const unsigned char *data"
.Fa "long len"
.Fc
.Ft int
.Fo PEM_read
.Fa "FILE *fp"
.Fa "char **name"
.Fa "char **header"
.Fa "unsigned char **data"
.Fa "long *len"
.Fc
.Ft int
.Fo PEM_read_bio
.Fa "BIO *bp"
.Fa "char **name"
.Fa "char **header"
.Fa "unsigned char **data"
.Fa "long *len"
.Fc
.Ft int
.Fo PEM_get_EVP_CIPHER_INFO
.Fa "char *header"
.Fa "EVP_CIPHER_INFO *cinfo"
.Fc
.Ft int
.Fo PEM_do_header
.Fa "EVP_CIPHER_INFO *cinfo"
.Fa "unsigned char *data"
.Fa "long *len"
.Fa "pem_password_cb *cb"
.Fa "void *userdata"
.Fc
.Ft int
.Fo PEM_def_callback
.Fa "char *password"
.Fa "int size"
.Fa "int verify"
.Fa "void *userdata"
.Fc
.Ft typedef int
.Fo pem_password_cb
.Fa "char *password"
.Fa "int size"
.Fa "int verify"
.Fa "void *userdata"
.Fc
.Sh DESCRIPTION
These functions read and write PEM-encoded objects, using the PEM type
.Fa name ,
any additional
.Fa header
information, and the raw
.Fa data
of length
.Fa len .
.Pp
PEM is the binary content encoding first defined in IETF RFC 1421.
The content is a series of base64-encoded lines, surrounded by
begin/end markers each on their own line.
For example:
.Bd -literal -offset indent
-----BEGIN PRIVATE KEY-----
MIICdg....
\&... bhTQ==
-----END PRIVATE KEY-----
.Ed
.Pp
Optional header line(s) may appear after the begin line, and their
existence depends on the type of object being written or read.
.Pp
.Fn PEM_write
writes to the file
.Fa fp ,
while
.Fn PEM_write_bio
writes to the BIO
.Fa bp .
The
.Fa name
is the name to use in the marker, the
.Fa header
is the header value or
.Dv NULL ,
and
.Fa data
and
.Fa len
specify the data and its length.
.Pp
The final
.Fa data
buffer is typically an ASN.1 object which can be decoded with the
.Fn d2i_*
function appropriate to the type
.Fa name ;
see
.Xr d2i_X509 3
for examples.
.Pp
.Fn PEM_read
reads from the file
.Fa fp ,
while
.Fn PEM_read_bio
reads from the BIO
.Fa bp .
Both skip any non-PEM data that precedes the start of the next PEM
object.
When an object is successfully retrieved, the type name from the
"----BEGIN <type>-----" is returned via the
.Fa name
argument, any encapsulation headers are returned in
.Fa header ,
and the base64-decoded content and its length are returned via
.Fa data
and
.Fa len ,
respectively.
The
.Fa name ,
.Fa header ,
and
.Fa data
pointers should be freed by the caller when no longer needed.
.Pp
The remaining functions are deprecated because the underlying PEM
encryption format is obsolete and should be avoided.
It uses an encryption format with an OpenSSL-specific key-derivation
function, which employs MD5 with an iteration count of 1.
Instead, private keys should be stored in PKCS#8 form, with a strong
PKCS#5 v2.0 PBE; see
.Xr PEM_write_PrivateKey 3
and
.Xr d2i_PKCS8PrivateKey_bio 3 .
.Pp
.Fn PEM_get_EVP_CIPHER_INFO
can be used to determine the
.Fa data
returned by
.Fn PEM_read
or
.Fn PEM_read_bio
is encrypted and to retrieve the associated cipher and IV.
The caller passes a pointer to a structure of type
.Vt EVP_CIPHER_INFO
via the
.Fa cinfo
argument and the
.Fa header
returned via
.Fn PEM_read
or
.Fn PEM_read_bio .
If the call is successful, 1 is returned and the cipher and IV are
stored at the address pointed to by
.Fa cinfo .
When the header is malformed or not supported or when the cipher is
unknown or some internal error happens, 0 is returned.
.Pp
.Fn PEM_do_header
can then be used to decrypt the data if the header indicates encryption.
The
.Fa cinfo
argument is a pointer to the structure initialized by a preceding call
to
.Fn PEM_get_EVP_CIPHER_INFO .
If that structure indicates the absence of encryption,
.Fn PEM_do_header
returns successfully without taking any action.
The
.Fa data
and
.Fa len
arguments are used both to pass in the encrypted data that was
returned in the same arguments from the preceding call to
.Fn PEM_read
or
.Fn PEM_read_bio
and to pass out the decrypted data.
.Pp
The callback function
.Fa cb
is used to obtain the encryption
.Fa password ;
if
.Fa cb
is
.Dv NULL ,
.Fn PEM_def_callback
is used instead.
The
.Fa password
buffer needs to be at least
.Fa size
bytes long.
Unless
.Fa userdata
is
.Dv NULL ,
.Fn PEM_def_callback
ignores the
.Fa verify
argument and copies the NUL-terminated byte string
.Fa userdata
to
.Fa password
without a terminating NUL byte, silently truncating the copy to at most
.Fa size
bytes.
If
.Fa userdata
is
.Dv NULL ,
.Fn PEM_def_callback
instead prompts the user for the password with echoing turned off
by calling
.Xr EVP_read_pw_string_min 3
internally.
In this case, the
.Fa size
is silently reduced to at most
.Dv BUFSIZ
and at most
.Fa size No \- 1
bytes are accepted from the user and copied into the byte string buffer
.Fa password .
A callback function
.Fa cb
supplied by the application may use
.Fa userdata
for a different purpose than
.Fn PEM_def_callback
does, e.g., as auxiliary data to use while acquiring the password.
For example, a GUI application might pass a window handle.
If the
.Fa verify
flag is non-zero, the user is prompted twice for the password to
make typos less likely and it is checked that both inputs agree.
This flag is not set by
.Fn PEM_do_header
nor by other read functions, but it is typically set by write functions.
.Pp
If the data is a priori known to not be encrypted, then neither
.Fn PEM_get_EVP_CIPHER_INFO
nor
.Fn PEM_do_header
need to be called.
.Sh RETURN VALUES
.Fn PEM_read
and
.Fn PEM_read_bio
return 1 on success or 0 on failure.
The latter includes the case when no more PEM objects remain in the
input file.
To distinguish end of file from more serious errors, the caller
must peek at the error stack and check for
.Dv PEM_R_NO_START_LINE ,
which indicates that no more PEM objects were found.
See
.Xr ERR_peek_last_error 3
and
.Xr ERR_GET_REASON 3 .
.Pp
.Fn PEM_get_EVP_CIPHER_INFO
and
.Fn PEM_do_header
return 1 on success or 0 on failure.
The
.Fa data
is likely meaningless if these functions fail.
.Pp
.Fn PEM_def_callback
returns the number of bytes stored into
.Fa buf
or a negative value on failure, and
.Fa cb
is expected to behave in the same way.
If
.Fa userdata
is
.Dv NULL ,
.Fn PEM_def_callback
fails if
.Fa num
is less than 5
or if an error occurs trying to prompt the user for the password.
Otherwise, it fails when
.Fa num
is negative.
The details of the circumstances that cause
.Fa cb
to fail may differ.
.Sh SEE ALSO
.Xr crypto 3 ,
.Xr d2i_PKCS8PrivateKey_bio 3 ,
.Xr PEM_ASN1_read 3 ,
.Xr PEM_bytes_read_bio 3 ,
.Xr PEM_read_bio_PrivateKey 3 ,
.Xr PEM_read_SSL_SESSION 3 ,
.Xr PEM_write_bio_CMS_stream 3 ,
.Xr PEM_write_bio_PKCS7_stream 3 ,
.Xr PEM_X509_INFO_read 3
.Sh HISTORY
.Fn PEM_write ,
.Fn PEM_read ,
and
.Fn PEM_do_header
appeared in SSLeay 0.4 or earlier.
.Fn PEM_get_EVP_CIPHER_INFO
first appeared in SSLeay 0.5.1.
.Fn PEM_write_bio
and
.Fn PEM_read_bio
first appeared in SSLeay 0.6.0.
These functions have been available since
.Ox 2.4 .
.Pp
.Fn PEM_def_callback
first appeared in OpenSSL 0.9.7 and has been available since
.Ox 3.2 .
